Polymer nano-strings

ABSTRACT

A polymer nano-string composition is provided. The polymer nano-strings can include a poly(alkenylbenzene) core, and a surface layer comprising poly(conjugated diene). The nano-strings have a mean average diameter of less than about 100 nm and a length of greater than about 1 μm.

This application is a divisional of U.S. Ser. No. 10/345,498, filed on16 Jan., 2003.

BACKGROUND OF THE INVENTION

The present invention relates to polymer nano-strings, methods for theirpreparation, and their use as, for example, additives for rubber,including natural and synthetic elastomers. The invention advantageouslyprovides several mechanisms for surface modifications,functionalization, and general characteristic tailoring to improveperformance in rubbers, elastomers, and thermoplastics.

Tires are often subjected to rough road conditions that producerepetitive, localized high-pressure pounding on the tire. These stressescan cause fatigue fracture and lead to crack formation and growth. Thisdegradation of the tire has also been referred to as chipping orchunking of the tread surface or base material.

In an attempt to prevent this degradation, it is known to addreinforcements such as carbon black, silicas, silica/silanes, or shortfibers. Silica has been found advantageous due to its ability to deflectand suppress cut prolongation, while silanes have been added to bind thesilica to unsaturated elastomers. The fibers that have been addedinclude nylon and aramid fibers.

It is also known that the addition of polyolefins to rubber compositionscan provide several beneficial properties. For example, low molecularweight high density polyethylene, and high molecular weight, low densitypolyethylene, are known to improve the tear strength of polybutadiene ornatural rubber vulcanizates. In the tire art, it has also been foundthat polyethylene increases the green, tear strength of carcasscompounds and permits easy extrusion in calendaring without scorch.Polypropylene likewise increases the green strength of butyl rubber.Polypropylene has also been effective in raising the static and dynamicmodulus of rubber, as well as its tear strength.

Although the addition of polyolefins to rubber compositions is known toprovide several beneficial effects, the addition of polyolefin to tirerecipes may also have a deleterious effect on other mechanical and wearproperties of tires, as well as handling and ride of the tire.

Polymer nano-particles have attracted increased attention over the pastseveral years in a variety of fields including catalysis, combinatorialchemistry, protein supports, magnets, and photonics. Similarly, vinylaromatic (e.g. polystyrene) microparticles have been prepared for usesas a reference standard in the calibration of various instruments, inmedical research and in medical diagnostic tests. Such polystyrenemicroparticles have been prepared by anionic dispersion polymerizationand emulsion polymerization.

Nano-particles preferably are monodisperse in size and uniform in shape.However, controlling the size of nano-particles during polymerizationand/or the surface characteristics of such nano-particles can bedifficult. Accordingly, achieving better control over the surfacecomposition of such polymer nano-particles also is desirable.

Nano-particles can serve as discrete particles uniformly dispersedthroughout a host composition. Rubbers may be advantageously modified bythe addition of various polymer compositions. The physical properties ofrubber moldability and tenacity are often improved through suchmodifications. Of course, however, the simple indiscriminate addition ofnano-particles to rubber is likely to cause degradation of the matrixmaterial, i.e., the rubber characteristics. Moreover, it is expectedthat the selection of nano-particles having suitable size, materialcomposition, and surface chemistry, etc., will improve the matrixcharacteristics. Polymer nano-strings may also serve as a reinforcementmaterial for rubber compositions in order to overcome theabove-mentioned drawbacks of polyolefin and silica reinforcement.Polymer nano-strings are capable of dispersing evenly throughout arubber composition, while maintaining a degree of entanglement betweenthe individual nano-strings, leading to improved reinforcement.

In this regard, development of polymer nano-strings having a surfacelayer which would be compatible with a wide variety of matrix materialsis desirable because discrete strings could likely disperse evenlythroughout the host to provide a uniform matrix composition. However,the development of a process capable of reliably producing acceptablenano-strings has been a challenging endeavor. Moreover, the developmentof a solution polymerization process producing reliable polymernano-strings advantageously employed in rubber compositions, has beenelusive.

SUMMARY OF THE INVENTION

A polymer nano-string composition including a poly(alkenylbenzene) coreand a surface layer of poly(conjugated diene) is provided. Thenano-strings have a mean average diameter of less than about 100 nm anda length of between about 1 and 1000 μm, the length being greater thanthe diameter. Preferably, the nano-strings have a length of at leastabout 10 μm.

A polymer nano-string including polyalkylene is provided. According tothe embodiment, these nano-strings include a poly(alkenylbenzene) coreand a polyalkylene surface layer including at least one alkylene monomerunit. The nano-strings have a mean average diameter less than about 100nm and a length between about 1 and 1000 μm.

A process for forming polymer nano-strings is also provided. The processincludes polymerizing alkenylbenzene monomer and conjugated dienemonomer in a hydrocarbon solvent to form a block copolymer. Afterformation of the block copolymer, a polymerization mixture includingworm-like micelles of the block copolymer is formed by adjusting theconcentration of the polymerization mixture until the solid content isbetween about 0.01 to 10% or between about 18 to 60%. At least onecrosslinking agent is then added to the polymerization mixture to formcrosslinked, polymer nano-strings having a rope-like structure andincluding an alkenylbenzene core and a conjugated diene surface from themicelles. The poly(conjugated diene) layer is optionally hydrogenated toform nano-strings containing a poly(alkenylbenzene) core and apolycrystalline outer layer.

A rubber compound composition containing the inventive nano-strings isprovided. Such compound shows its relatively high hysterisis, goodtensile strength, strong resistance to creep, and high temperatureresistance. A process of making the rubber compound is similarlyprovided.

Herein throughout, unless specifically stated otherwise:

-   -   i. “vinyl-substituted aromatic hydrocarbon” and “alkenylbenzene”        are used interchangeably; and    -   ii. “rubber” refers to rubber compounds, including natural        rubber, and synthetic elastomers including styrene-butadiene        rubber, ethylene propylene rubber, etc., which are known in the        art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the design structure of anano-string and a cross-section view thereof, according to the presentinvention.

FIG. 2 is an atomic force microscopy photograph of polymer nano-strings,on a mica-surface, produced according to the present invention.

FIG. 3 is a transmission electron microspcopy photograph of a singlepolymer nano-string produced according to the present invention.

FIG. 4 is a transmission electron microscopy photograph of multipletangled nano-strings produced according to the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

General Nano-Particle Process of Formation

This application incorporates by reference U.S. Pat. No. 6,437,050, U.S.Ser. No. 10/038,748 (filed Dec. 31, 2001) and Ser. No. 10/223,393 (filedAug. 19, 2002).

One exemplary polymer nano-string of the present invention is formedfrom diblock copolymer chains having a poly(conjugated diene) block anda poly(alkenylbenzene) block. The poly(alkenylbenzene) blocks may becrosslinked to form the desired nano-strings. The nano-strings havediameters—expressed as a mean average diameter—that are preferably lessthan about 100 nm, more preferably less than about 75 nm, and mostpreferably less than about 50 nm. The nano-strings have a rope-likeshape, with a length of between about 1 and 1000 μm, more preferablybetween about 2 and 100 μm. The nano-strings preferably retain theirdiscrete nature with little or no polymerization between strings. Thenano-particles preferably are substantially monodisperse and uniform inshape.

The nano-stings preferably have a high glass-transition temperature(T_(g)), contributing to the improved reinforcement capabilities.Preferably, the T_(g) is between about 50 and 220° C., more preferablybetween about 90 and 200° C.

The nano-strings are preferably formed by dispersion polymerization,although emulsion polymerization is also contemplated. Hydrocarbons arepreferably used as the dispersion solvent. Suitable solvents includealiphatic hydrocarbons, such as pentane, hexane, heptane, octane,nonane, decane, and the like, as well as alicyclic hydrocarbons, such ascyclohexane, methyl cyclopentane, cyclooctane, cyclopentane,cycloheptane, cyclononane, cyclodecane, and the like. These hydrocarbonsmay be used individually or in combination. However, as more fullydescribed herein below, selection of a solvent in which one polymerforming the nano-particles is more soluble than another polymer formingthe nano-particles is beneficial to micelle formation.

With respect to the monomers and solvents identified herein,nano-strings can be formed by maintaining a temperature andconcentration that is favorable to polymerization of the selectedmonomers in the selected solvent(s). Preferred temperatures are in therange of about −40 to 250° C., with a temperature in the range of about0 to 150° C. being particularly preferred. As described in more detailbelow, the interaction of monomer selection, temperature, and solventfacilitates the formation of diblock polymers which form worm-likemicelles and ultimately the desired polymer nano-strings.

According to one embodiment of the invention, a diblock copolymer isformed of vinyl aromatic hydrocarbon monomers and conjugated dienemonomers in a hydrocarbon solvent. The diblock copolymer contains atleast a first block that is substantially soluble in the hydrocarbonsolvent, preferably a conjugated diene monomer, and a second block whichis less soluble in the hydrocarbon solvent, preferably avinyl-substituted aromatic hydrocarbon monomer. Moreover, in onepreferred embodiment, a vinyl-substituted aromatic hydrocarbon monomeris chosen, the polymer of which is insoluble in the dispersion solvent.

As is known in the art, such a diblock copolymer may be formed by livinganionic polymerization, in which a vinyl-substituted aromatichydrocarbon monomer is added to a completely polymerized conjugateddiene monomer. Another method of forming substantially diblockcopolymers is the living anionic copolymerization of a mixture of aconjugated diene monomer and a vinyl-substituted aromatic hydrocarbonmonomer in a hydrocarbon solvent, particularly, in the absence ofcertain polar additives, such as ethers, tertiary amines, or metalalkoxides which could otherwise effect the polymerization of theseparately constituted polymer blocks. Under these conditions, theconjugated diene generally polymerizes first, followed by thepolymerization of the vinyl-substituted aromatic hydrocarbon. Of course,certain advantages, as described below, may be achieved via a randompolymerization of at least one block of the polymer.

Nonetheless, it is generally preferred that a conjugated diene blockpolymerize first, followed by a vinyl-substituted aromatic, positioningthe living end of the polymerizing polymer on the vinyl aromatic blockto facilitate later crosslinking.

Such copolymers, formed by either method, are believed to aggregate toform micelle-like structures, with for example, the vinyl-substitutedaromatic blocks directed toward the center of the micelle and theconjugated diene blocks extending as tails therefrom. By maintaining arelatively higher ratio of vinyl-substituted aromatic block toconjugated diene, a worm-like micelle shape is formed. The micelleformation may also be controlled by the maintenance of favorable solidscontent and favorable polymerization temperatures. For example, afurther hydrocarbon charge may be made to control the solids content ofthe polymerization mixture. A preferred solids content is between about0.01 and 50%, with a solids content between about 0.1-10% or about 18 to60% being more preferred. The control of the solids content within thedesirable range is believed to help achieve formation of the desiredworm-like shape of the micelles. Moreover, these steps may be used totake advantage of the general insolubility of the vinyl-aromatic blocks.An exemplary temperature range for micelle formation is between about 40and 150° C., more preferably between about 40 and 120° C., and mostpreferably between about 50 and 100° C.

After the micelles have formed, additional conjugated diene monomerand/or vinyl-substituted aromatic hydrocarbon monomer can be added tothe polymerization mixture as desired.

After formation of the micelles, a cross-linking agent is added to thepolymerization mixture. Preferably, a crosslinking agent is selectedwhich has an affinity for the vinyl-substituted aromatic hydrocarbonmonomer blocks and migrates to the center of the micelles due to itscompatibility with those monomer units and initiator residues present inthe center of the micelle and its relative incompatibility with thedispersion solvent and monomer units present in the outer layer of themicelle. The crosslinking agent crosslinks the center core of themicelle (i.e. alkenylbenzene) to form the derived polymer nano-strings.Consequently, nano-strings are formed from the micelles with a coreincluding, for example, cross-linked styrene monomer units, a styrenemonomer unit layer and a shell layer including, for example butadienemonomer units (see FIG. 1).

The conjugated diene monomers contemplated for the diblock copolymer arethose soluble in non-aromatic hydrocarbon solvents. C₄-C₈ conjugateddiene monomers are the preferred. Exemplary conjugated diene monomersinclude 1,3-butadiene, isoprene, and 1,3-pentadiene.

Vinyl-substituted aromatic hydrocarbon monomers include styrene,α-methyl-styrene, 1-vinyl naphthalene, 2-vinyl naphthalene, vinyltoluene, methoxystyrene, t-butoxystyrene, and the like, as well asalkyl, cycloalkyl, aryl, alkaryl, and aralkyl derivatives thereof, inwhich the total number of carbon atoms in the combined hydrocarbon isgenerally not greater than about 18, as well as any di- or tri-vinylsubstituted aromatic hydrocarbons, and mixtures thereof.

The diblock copolymer preferably has a M_(w) of about 5,000 to about200,000, more preferably between about 10,000 and about 100,000. Atypical diblock polymer will be comprised of about 5 to 95% by weightconjugated diene and about 95-5% by weight vinyl-substituted aromatichydrocarbon, more preferably about 20-80% by weight, and most preferably40-60% by weight of each contributed monomer type. However, to form theworm-like micelle structure, it may be beneficial to use more by weightvinyl-substituted aromatic hydrocarbon than conjugated diene. Thispreference is not absolute as solvent selection, temperature of reactionand solids content, as outlined above, can also contribute to theformation of worm-like micelles.

The micelle formed by the polymerization of vinyl-substituted aromatichydrocarbons and conjugated diene monomers is preferably crosslinked toenhance the permanence of shape and size of the resultant nano-strings.Preferred crosslinking agents are di-or tri-vinyl-substituted aromatichydrocarbons. However, crosslinking agents which are at leastbifunctional, wherein the two functional groups are capable of reactingwith vinyl-substituted aromatic hydrocarbon monomers are acceptable. Apreferred crosslinking agent is divinylbenzene (DVB).

Without being bound by theory, it is believed that an exemplaryworm-like micelle will be comprised of one hundred to five billiondiblock polymers yielding, after crosslinking, a nano-string having adiameter between about 1 and 100 nm and a length between about 1 and1000 μm.

A 1,2-microstructure controlling agent or randomizing modifier isoptionally used to control the 1,2-microstructure in the conjugateddiene contributed monomer units, such as 1,3-butadiene, of thenano-strings. Suitable modifiers include hexamethylphosphoric acidtriamide, N,N, N′,N′-tetramethylethylene diamine, ethylene glycoldimethyl ether, diethylene glycol dimethyl ether, triethylene glycoldimethyl ether, tetraethylene glycol dimethyl ether, tetrahydrofuran,1,4-diazabicyclo[2.2.2]octane, diethyl ether, triethylamine,tri-n-butylamine, tri-n-butylphosphine, p-dioxane, 1,2 dimethoxy ethane,dimethyl ether, methyl ethyl ether, ethyl propyl ether, di-n-propylether, di-n-octyl ether, anisole, dibenzyl ether, diphenyl ether,dimethylethylamine, bix-oxalanyl propane, tri-n-propyl amine, trimethylamine, triethyl amine, N,N-dimethyl aniline, N-ethylpiperidine,N-methyl-N-ethyl aniline, N-methylmorpholine, tetramethylenediamine,oligomeric oxolanyl propanes (OOPs), 2,2-bis-(4-methyl dioxane),bistetrahydrofuryl propane, and the like. A mixture of one or morerandomizing modifiers also can be used. The ratio of the modifier to themonomers can vary from a minimum as low as 0 to a maximum as great asabout 400 millimoles, preferably about 0.01 to about 3000 millimoles, ofmodifier per hundred grams of monomer currently being charged into thereactor. As the modifier charge increases, the percentage of1,2-microstructure (vinyl content) increases in the conjugated dienecontributed monomer units in the surface layer of the nano-strings. The1,2-microstructure content of the conjugated diene units is preferablybetween about 1 and 99%, more preferably between about 5 and 95%.

Structural Modifications

In an alternative embodiment, the surface layer of the polymernano-strings includes a copolymer including at least one alkenylbenzenemonomer unit and at least one conjugated diene monomer unit. Thecopolymer may be random or ordered. Accordingly, the surface layer mayinclude an SBR rubber. Herein throughout, references to apoly(conjugated diene) surface layer are understood to includecopolymers of the type described here.

The density of the poly(conjugated diene) surface layer of thenano-strings may be controlled by manipulating the ratio of diblock tomono-block polymer chains. This ratio may be manipulated by altering theamount of initiator added during each step of the polymerizationprocess. For example, a greater amount of initiator added during thepolymerization of the conjugated diene monomer than added during thepolymerization of the alkenylbenzene monomer would favor diblockformation over mono-block formation, resulting in a high density surfacelayer. Conversely, a greater amount of initiator added during thepolymerization of the alkenylbenzene monomer than added during thepolymerization of the conjugated diene monomer would favor mono-blockformation over diblock formation, resulting in a low-density surfacelayer. The ratio of mono-blocks to diblocks can be from 1 to 99,preferably 10 to 90, more preferably 20 to 80.

Hydrogenation of a Nano-String Surface Layer

After crosslinking, the polydiene blocks may be hydrogenated to form amodified surface layer. A hydrogenation step may be carried out bymethods known in the art for hydrogenating polymers, particularlypolydienes. A preferred hydrogenation method includes placing thecrosslinked nano-strings in a hydrogenation reactor in the presence of acatalyst. After the catalyst has been added to the reactor, hydrogen gas(H₂) is charged to the reactor to begin the hydrogenation reaction. Thepressure is adjusted to a desired range via addition of H₂, preferablybetween about 10 and 3000 kPa, more preferably between about 50 and 2600kPa. H₂ may be charged continuously or in individual charges until thedesired conversion is achieved. Preferably, the hydrogenation reactionwill reach at least about 20% conversion, more preferably greater thanabout 85% conversion. The conversion reaction may be monitored by H¹NMR.

Preferred catalysts include known hydrogenation catalysts such as Pt,Pd, Rh, Ru, Ni, and mixtures thereof. The catalysts may be finelydispersed solids or absorbed on inert supports such as carbon, silica,or alumina. Especially preferred catalysts are prepared from nickeloctolate, nickel ethylhexanoate, and mixtures thereof.

The surface layer formed by an optional hydrogenation step will varydepending on the identity of the monomer units utilized in the formationof the nano-string surface layer, particularly the poly(conjugateddiene) blocks. For example, if the poly(conjugated diene) block contains1,3-butadiene monomer units, the resultant nano-string layer afterhydrogenation will be a crystalline poly(ethylene) layer. In anotherembodiment, a layer may include both ethylene and propylene units afterhydrogenation if the non-hydrogenated poly(conjugated diene) blockcontains isoprene monomer units. It should be noted that thenon-hydrogenated poly(conjugated diene) block may contain a mixture ofconjugated diene monomer units, or even alkenylbenzene units, resultingin a mixture of monomer units after hydrogenation.

Initiators and Functionalized Nano-Strings

The present inventive process is preferably initiated via addition ofanionic initiators that are known in the art as useful in thecopolymerization of diene monomers and vinyl aromatic hydrocarbons.Exemplary organo-lithium catalysts include lithium compounds having theformula R(Li)_(x), wherein R represents a C₁-C₂₀ hydrocarbyl radical,preferably a C₂-C₈ hydrocarbyl radical, and x is an integer from 1 to 4.Typical R groups include aliphatic radicals and cycloaliphatic radicals.Specific examples of R groups include primary, secondary, and tertiarygroups, such as n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, etc.

Specific examples of exemplary initiators include ethyllithium,propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, andthe like; aryllithiums, such as phenyllithium, tolyllithium, and thelike; alkenyllithiums such as vinyllithium, propenyllithium, and thelike; alkylene lithium such as tetramethylene lithium, pentamethylenelithium, and the like. Among these, n-butyllithium, sec-butyllithium,tert-butyllithium, tetramethylene lithium, and mixtures thereof arepreferred. Other suitable lithium initiators include one or more of:p-tolyllithium, 4-phenylbutyl lithium, 4-butylcyclohexyl lithium,4-cyclohexylbutyl lithium, lithium dialkyl amines, lithium dialkylphosphines, lithium alkyl aryl phosphine, and lithium diaryl phosphines.

Functionalized lithium initiators are also contemplated as useful in thepresent copolymerization. Preferred functional groups include amines,formyl, carboxylic acids, alcohol, tin, silicon, silyl ether andmixtures thereof.

Especially preferred initiators are amine-functionalized initiators,such as those that are the reaction product of an amine, an organolithium and a solubilizing component. The initiator has the generalformula:(A)Li(SOL)_(y)where y is from about 1 to about 3; SOL is a solubilizing componentselected from the group consisting of hydrocarbons, ethers, amines ormixtures thereof; and, A is selected from the group consisting of alkyl,dialkyl and cycloalkyl amine radicals having the general formula:

and cyclic amines having the general formula:

where R¹ is selected from the group consisting of alkyls, cycloalkyls oraralkyls having from 1 to about 12 carbon atoms, and R² is selected fromthe group consisting of an alkylene, substituted alkylene, oxy- orN-alkylamino-alkylene group having from about 3 to about 16 methylenegroups. An especially preferred functionalized lithium initiator ishexamethylene imine propyllithium.

Tin functionalized lithium initiators may also be preferred as useful inthe present invention. Suitable tin functionalized lithium initiatorsinclude tributyl tin lithium, triocty tin lithium, and mixtures thereof.

Anionic initiators generally are useful in amounts ranging from about0.01 to 60 millimoles per hundred grams of monomer charge.

A nano-string including diblock copolymers initiated with afunctionalized initiator may include functional groups on the surface ofthe nano-string. For example, when block polymers are initiated byhexamethylene imine propyllithium, the initiator residue remaining atthe beginning of the polymer chain will contain an amine group. Once thepolymer chains have aggregated and have been crosslinked, the resultantnano-strings will contain amine groups on or near the nano-stringsurface.

An exemplary nano-string formed from copolymers initiated by afunctionalized tin lithium initiator may have a crosslinkedalkenylbenzene core, for example polystyrene, and a surface layerincluding at least a poly(conjugated diene), for example 1,3-butadiene.The surface layer will also include a functionalized initiator residueat the individual chain ends (e.g., tin).

Polymer Nano-String Applications

A variety of applications are contemplated for use in conjunction withthe rope-like nano-strings of the present invention. Furthermore, theseveral mechanisms described herein for modifying the polymernano-strings render them suitable for different applications. All formsof the present inventive nano-strings are, of course, contemplated foruse in each of the exemplary applications and all other applicationsenvisioned by the skilled artisan.

General Rubber

After the polymer nano-strings have been formed, they may be blendedwith a rubber to improve the physical characteristics of the rubbercomposition. Nano-strings are useful modifying agents for rubbersbecause they are capable of dispersing uniformly throughout the rubbercomposition, resulting in uniformity of physical characteristics.Furthermore, certain of the present polymer nano-strings areadvantageous because the surface layer of poly(conjugated diene),especially vinyl-modified poly(conjugated diene), is capable of bondingwith the rubber matrix due to the accessibility of the double bonds inthe poly(conjugated diene).

The present polymer nano-strings are suitable for modifying a variety ofrubbers including, but not limited to, random styrene/butadienecopolymers, butadiene rubber, poly(isoprene), nitrile rubber,polyurethane, butyl rubber, EPDM, and the like. Advantageously, theinclusion of the present nano-strings have demonstrated rubbers havingimproved tensile and tear strength of at least about 30% over the baserubber.

Furthermore, nano-strings with hydrogenated surface layers maydemonstrate improved compatibility with specific rubbers. For example,nano-strings including a hydrogenated polyisoprene surface layer maydemonstrate superior bonding with and improved dispersion in an EPDMrubber matrix due to the compatibility of hydrogenated isoprene withEPDM rubber.

Additionally, nano-strings with copolymer surfaces may demonstrateimproved compatibility with rubbers. The copolymer tails with thesurface layer of the nano-strings may form a brush-like surface. Thehost composition is then able to diffuse between the tails allowingimproved interaction between the host and the nano-strings.

Hard Disk Technology

Hydrogenated nano-strings prepared in accordance with the presentinvention may also find application in hard disk technology.

Disk drive assemblies for computers traditionally include a magneticstorage disk coaxially mounted about a spindle apparatus that rotates atspeeds in excess of several thousand revolutions per minute (RPM). Thedisk drive assemblies also include a magnetic head that writes and readsinformation to and from the magnetic storage disk while the magneticdisk is rotating. The magnetic head is usually disposed at the end of anactuator arm and is positioned in a space above the magnetic disk. Theactuator arm can move relative to the magnetic disk. The disk driveassembly is mounted on a disk base (support) plate and sealed with acover plate to form a housing that protects the disk drive assembly fromthe environmental contaminant outside of the housing.

Serious damage to the magnetic disks, including loss of valuableinformation, can result by introducing gaseous and particulatecontaminates into the disk drive assembly housing. To substantiallyprevent or reduce the introduction of gaseous and particulatecontaminants into the disk drive housing, a flexible sealing gasket isdisposed between the disk drive mounting base (support) plate and thedisk drive assembly housing or cover plate. A sealing gasket is usuallyprepared by punching out a ring-shaped gasket from a sheet of curedelastomer. The elastomeric gasket obtained is usually attached to thebase plate of the disk drive assembly mechanically, such as affixing thegasket with screws, or adhesives. The hydrogenated nano-strings, whencompounded with a polyalkylene and a rubber, demonstrate a tensilestrength comparable to that necessary in hard disk drive compositions.

Thermoplastic Gels

Nano-strings prepared in accord with the present invention, whetherhydrogenated or non-hydrogenated may also be blended with a variety ofthermoplastic elastomers, such as SEPS, SEBS, EEBS, EEPE, polypropylene,polyethylene, and polystyrene. For example, nano-particles withhydrogenated isoprene surface layers may be blended with a SEPSthermoplastic to improve tensile strength and thermostability. Theseblends of thermoplastic elastomer and nano-particles would typically beextended as known in the art. For example, suitable extenders includeextender oils and low molecular weight compounds or components. Suitableextender oils include those well known in the art such as naphthenic,aromatic and paraffinic petroleum oils and silicone oils.

Examples of low molecular weight organic compounds or components usefulas extenders in compositions of the present invention are low molecularweight organic materials having a number-average molecular weight ofless than 20,000, preferably less than 10,000, and most preferably lessthan 5,000. Although there is no limitation to the material which may beemployed, the following is a list of examples of appropriate materials:

-   -   (1) Softening agents, namely aromatic naphthenic and paraffinic        softening agents for rubbers or resins;    -   (2) Plasticizers, namely plasticizers composed of esters        including phthalic, mixed pthalic, aliphatic dibasic acid,        glycol, fatty acid, phosphoric and stearic esters, epoxy        plasticizers, other plasticizers for plastics, and phthalate,        adipate, scbacate, phosphate, polyether and polyester        plasticizers for NBR;    -   (3) Tackifiers, namely coumarone resins, coumaroneindene resins,        terpene phenol resins, petroleum hydrocarbons and rosin        derivative;    -   (4) Oligomers, namely crown ether, fluorine-containing        oligomers, polybutenes, xylene resins, chlorinated rubber,        polyethylene wax, petroleum resins, rosin ester rubber,        polyalkylene glycol diacrylate, liquid rubber (polybutadiene,        styrene/butadiene rubber, butadiene-acrylonitrile rubber,        polychloroprene, etc.), silicone oligomers, and poly-a-olefins;    -   (5) Lubricants, namely hydrocarbon lubricants such as paraffin        and wax, fatty acid lubricants such as higher fatty acid and        ydroxyl-fatty acid, fatty acid amide lubricants such as fatty        acid amide and alkylene-bisfatty acid amide, ester lubricants        such as fatty acid-lower alcohol ester, fatty acid-polyhydrie        alcohol ester and fatty acid-polyglycol ester, alcoholic        lubricants such as fatty alcohol, polyhydric alcohol, polyglycol        and polyglycerol, metallic soaps, and mixed lubricants; and,    -   (6) Petroleum hydrocarbons, namely synthetic terpene resins,        aromatic hydrocarbon resins, aliphatic hydrocarbon resins,        aliphatic or alicyclic petroleum resins, polymers of unsaturated        hydrocarbons, and hydrogenated hydrocarbon resins.

Other appropriate low-molecular weight organic materials includelatexes, emulsions, liquid crystals, bituminous compositions, andphosphazenes. One or more of these materials may be used in asextenders.

Tire Rubber

One application for nano-string containing rubber compounds is in tirerubber formulations.

Vulcanizable elastomeric compositions of the invention can be preparedby mixing a rubber, a nano-string composition, with a reinforcing fillercomprising silica, or a carbon black, or a mixture of the two, aprocessing aid and/or a coupling agent, a cure agent and an effectiveamount of sulfur to achieve a satisfactory cure of the composition.

The preferred rubbers are conjugated diene polymers, copolymers orterpolymers of conjugated diene monomers and monovinyl aromaticmonomers. These can be utilized as 100 parts of the rubber in the treadstock compound, or they can be blended with any conventionally employedtreadstock rubber which includes natural rubber, synthetic rubber andblends thereof. Such rubbers are well known to those skilled in the artand include synthetic polyisoprene rubber, styrene-butadiene rubber(SBR), styrene-isoprene rubber, styrene-isoprene-butadiene rubber,butadiene-isoprene rubber, polybutadiene, butyl rubber, neoprene,acrylonitrile-butadiene rubber (NBR), silicone rubber, thefluoroelastomers, ethylene acrylic rubber, ethylene-propylene rubber,ethylene-propylene terpolymer (EPDM), ethylene vinyl acetate copolymer,epicholrohydrin rubber, chlorinated polyethylene-propylene rubbers,chlorosulfonated polyethylene rubber, hydrogenated nitrile rubber,terafluoroethylene-propylene rubber, and the like.

Examples of reinforcing silica fillers which can be used in thevulcanizable elastomeric composition include wet silica (hydratedsilicic acid), dry silica (anhydrous silicic acid), calcium silicate,and the like. Other suitable fillers include aluminum silicate,magnesium silicate, and the like. Among these, precipitated amorphouswet-process, hydrated silicas are preferred. Silica can be employed inthe amount of about one to about 100 parts per hundred parts of theelastomer (phr), preferably in an amount of about 5 to 80 phr and, morepreferably, in an amount of about 30 to about 80 phrs. The useful upperrange is limited by the high viscosity imparted by fillers of this type.Some of the commercially available silica which can be used include, butare not limited to, HiSil® 190, HiSil® 210, HiSil® 215, HiSil® 233,HiSil® 243, and the like, produced by PPG Industries (Pittsburgh, Pa.).A number of useful commercial grades of different silicas are alsoavailable from DeGussa Corporation (e.g., VN2, VN3), Rhone Poulenc(e.g., Zeosil® 1165 MP0), and J. M. Huber Corporation.

Including surface functionalized nano-strings in silica containingrubber compositions can also decrease the shrinkage rates of such silicacontaining rubber compositions. Functionalized nano-particles may becompounded in silica compositions in concentrations up to about 30 wt %of the total composition, more preferably up to about 40 wt %, mostpreferably up to about 50 wt %.

The rubber can be compounded with all forms of carbon black, optionallyadditionally with silica. The carbon black can be present in amountsranging from about one to about 100 phr. The carbon black can includeany of the commonly available, commercially-produced carbon blacks, butthose having a surface are of at least 20 m²/g and, or preferably, atleast 35 m²/g up to 200 m²/g or higher are preferred. Among usefulcarbon blacks are furnace black, channel blacks, and lamp blacks. Amixture of two or more of the above blacks can be used in preparing thecarbon black products of the invention. Typical suitable carbon blackare N-110, N-220, N-339, N-330, N-352, N-550, N-660, as designated byASTM D-1765-82a.

Certain additional fillers can be utilized including mineral fillers,such as clay, talc, aluminum hydrate, aluminum hydroxide and mica. Theforegoing additional fillers are optional and can be utilized in theamount of about 0.5 phr to about 40 phr.

Numerous coupling agent and compatibilizing agent are know for use incombining silica and rubber. Among the silica-based coupling andcompatibilizing agents include silane coupling agents containingpolysulfide components, or structures such as, for example,trialkoxyorganosilane polysulfides, containing from about 2 to about 8sulfur atoms in a polysulfide bridge such as, for example,bis-(3-triethoxysilylpropyl) tetrasulfide (Si69),bis-(3-triethoxysilylpropyl)disulfide (Si75), and those alkylalkoxysilanes of the such as octyltriethoxy silane, and hexyltrimethoxysilane.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various vulcanizablepolymer(s) with various commonly used additive materials such as, forexample, curing agents, activators, retarders and acceleratorsprocessing additives, such as oils, resins, including tackifying resins,plasticizers, pigments, additional filers, fatty acid, zinc oxide,waxes, antioxidants, anti-ozonants, and peptizing agents. As known tothose skilled in the art, depending on the intended use of the sulfurvulcanizable and sulfur vulcanized material (rubbers), the additivesmentioned above are selected and commonly used in the conventionalamounts.

Specifically, the above-described nano-string containing rubbercompounds are contemplated for use in rubber compounds used to make tiretreads and side walls due to the enhanced reinforcement capabilities ofthe present nano-particles. The higher dynamic modulus (G′) and itslower temperature dependence along with the lower hysteresis values athigh temperature leads to the improved cornering, handling, dry, snow,and wet traction, rolling resistance, dispersion, and aging propertiesof the resultant tire compositions. Improved aging properties, thermalaging (high temperature), or mechanical aging (static or dynamicdeformation cycles), include retention of the G′ modulus, hysteresis,mechanical strengths, etc. Tin-functionalized nano-particles areespecially suited for use in tire compositions. Nano-strings including acopolymer surface layer are also suitable for use in such tirecompositions, because the longer copolymer chains in the surface layerleads to greater diffusion of the host rubber composition into thesurface layer of the nano-string. Of course, the functionalizednano-string having a copolymer surface layer, i.e., the combination ofthe two alternatives may be most beneficial.

Engineering Plastics and Others

Similarly, the nano-strings can be added into typical plastic materials,including polyethylene, polypropylene, polystyrene, polycarbonate,nylon, polyimides, etc. to for example, enhance impact strength, tensilestrength and damping properties.

Of course, the present inventive nano-strings are also suited to otherpresently existing applications for nano-strings, including the medicalfield, e.g. drug delivery and blood applications, informationtechnology, e.g. quantum computers and dots, aeronautical and spaceresearch, energy, e.g., oil refining, and lubricants.

Engine Mount, Etc.

Another application for such rubbers is in situations requiring superiordamping properties, such as engine mounts and hoses (e.g. airconditioning hoses). Rubber compounds of high mechanical strength, superdamping properties, and strong resistance to creep are demanded inengine mount manufacturers. In engine mounts, a rubber, because it sitsmost of its life in a packed and hot position, requires very goodcharacteristics. Utilizing the nano-strings within selected rubberformulations can improve the characteristics of the rubber compounds.

The present invention now will be described with reference tonon-limiting examples. The following examples and tables are presentedfor purposes of illustration only and are not to be construed in alimiting sense.

EXAMPLES

Preparation of Polymers

A 7.6 L reactor equipped with external jacked heating and internalagitation was used for all polymerizations. 1,3-Butadiene was used as a22.0 weight percent solution in hexane. Styrene was used as a 33 wt. %solution in hexane, and n-butlyithium was used as a 15 M solution inhexane. Technical grade divinylbenzene (DVB, 80% as a mixture ofisomers, Aldrich) was passed through a column of inhibitor remover underN₂ before use.

Example 1

Preparation of Polymer Nano-Strings

The reactor was charged with 1.2 kg of 22% butadiene and heated to 57°C. After the temperature had stabilized, polymerization was initiatedwith 10.2 mL of a 1.5 M butyllithium/hexane solution. The batchtemperature was maintained at 57° C. for the duration of thepolymerization. After 2 hours, the reactor was charged with 1.8 kg of33% styrene. After an additional 2 hour reaction time, the reactor wascharged with 140 mL of divinylbenzene. After 10 minutes, the agitationwas stopped and the temperature was maintained at 57° C. for anadditional 2 hours. The reactor was then discharged and the product wasdropped into a 95:5 acetone: isopropanol bath and the product was dried.

GPC analysis showed that before adding the DVB, the intermediate polymerhad a M_(w) of about 46,744. The polydispersity of the segment was about1.08. The final product was delaminated by transmission electronmicroscopy (TEM). For TEM analysis, about 10 mL of solution was takenfrom the batch and further diluted with the hexane solvent to about 14wt %. A drop of the diluted solution was then coated on a graphed coppermicro-screen and the solvent was evaporated. The screen was thenexamined by TEM. The results showed that the product was composed ofpolymer nano-strings. The diameter of the nano-strings was about 20 nm.The length of the nano-strings ranged from about 0.1 to 20 μm. Moreparticularly, FIG. 2 shows the nano-strings via atomic force microscopyon a mica surface. FIG. 3 shows a single nano-string via electronmicroscopy and FIG. 4 shows multiple tangled nano-strings via electronmicroscopy.

Examples 2-4

Application of Polymer Nano-Strings in Rubber Compositions

Two kinds of rubber compositions were prepared according to theformulation shown in Tables 1 and 2 by selectively using the synthesizednano-strings to replace the amount of polubutadiene in the compoundformulation (i.e., example 3) or by adding the synthesized nano-stringsdirectly into the compound (i.e., example 2). One control was used(i.e., example 4) for setting up a comparison with the test compounds.In each sample, a blend of the ingredients was kneaded by a methodlisted in Table 3. The final stock was sheeted and molded at 160° C. for30 minutes.

On the vulcanized rubber compounds of Examples 2-4, measurement of thetensile strength, tear strength, hysterisis loss gave the results asshown in Table 4. Measurement of tensile strength is based on conditionsof ASTM-D 412 at 22° C. Test specimen geometry was taken in the form ofa ring of a width of 0.125 cm and a thickness of 0.191 cm. The specimentested at a specific gauge length of 2.54 cm. The measurement of tearstrength is based on conditions of ASTM-D 624 at 170° C. Test specimengeometry was taken in the form of a nicked ring (ASTM-624-C). Thespecimen was tested at the specific gauge length of 4.45 inches. Thehysteresis loss was measured with a Dynastat Viscoelastic Analyzer. Testspecimen geometry was taken in the form of a strip of a length of 30 mmand of a width of 15 mm. The following testing conditions were employed:frequency 5 Hz, 2% strain. Measurement of the wet traction (StanleyLondon) was performed on the British Portable Skid Tester [see the RoadResearch Laboratory Technical Paper No. 66 by C. G. Giles et al. London,(1966)]. The sample geometry for the test is a rectangle bar of2.54×7.62×0.64 cm.

As can be seen in the Table 4, the rubber composition of examples 2 and3 exhibited well balanced physical properties. The tensile strength andthe tear strength of the modified rubber compounds are better than thatof the comparative compounds (i.e., Example 4) under equal moduluscondition. The dynamic modulus measurements of examples 2 and 3 are muchhigher than that of the control, indicating that the test compoundspossess improved traction. TABLE 1 Composition for Master BatchComponent pbw Polybutadiene 100.00 Carbon Black (N343) 50.00 AromaticOil 15.00 Zinc Oxide 3.00 Hydrocarbon Resin (tackifiers) 2.00 Santoflex13 (antioxidants) 0.95 Stearic Acid 2.00 Wax 1.00

TABLE 2 Composition for Final Batch additional component added to MasterBatch pbw Sulfur ˜1.30 Cyclohexyl-benzothiazole sulfenamide(accelerator) 1.40 Diphenylguanidine (accelerator) 0.20

TABLE 3 Mixing Conditions Mixer: 300 g Brabender Agitation Speed: 60 rpmMaster Batch Stage Initial Temperature 110° C.   0 min charging polymers5.0 min Drop Final Batch Stage Initial Temperature  75° C.   0 secCharging master stock  30 sec Charging curing agent and accelerators  75sec Drop

TABLE 4 A Summary on the Experimental Results Example 4 Example 2Example 3 (comparative) Nano-string 10 10 0 (example 1) (pbw)polybutadiene (pbw) 100 90 100 carbon black (pbw) 50 50 50 aromatic oil(pbw) 15 15 15 130° C. ML4 40.79 42.11 41.58 Shore A 22° C. (3 sec) 60.564.5 58.7 Shore A 100° C. (3 56.4 59.9 58.1 sec) Ring Tensile Test  23°C. Tb (kPa) 11,830 14,214 12,402 Eb (%) 484 464 410 M300 880 1128 1125M50 171 203 165 100° C. Tb (kPa) 5,650 6,670 6,738 Eb (%) 484 464 410M300 690 863 M50 120 138 149 Strength (kg/cm) 342 358 337 Ring Teartravel (%) 482 416 359 170° C. Tg of Compound −77 −75 −75 (° C.) StanleyLondon 46 48 47 (concrete) Dynastat M′50° C. 10.8240 13.519 7.8638 tan ┘50° C. 0.21772 0.21681 0.15379 M′ 23° C. 14.019 18.118 8.9348 tan ┘ 23°C. 0.23054 0.22521 0.18035 M′ 0° C. 17.103 22.762 10.519 tan ┘ 0° C.0.24068 0.23099 0.20378 M′ −20° C. 21.512 28.977 11.785 tan ┘ −20° C.0.24679 0.22815 0.23035

The invention has been described with reference to the exemplaryembodiments. Modifications and alterations will occur to others uponreading and understanding the specification. The invention is intendedto include such modifications and alterations insofar as they comewithin the scope of the disclosure and claims.

1. A process for forming polymer nano-strings comprising: a.polymerizing alkenylbenzene and conjugated diene monomer in ahydrocarbon solvent to form a diblock polymer; b. forming a mixtureincluding micelles of said diblock polymer; c. adjusting a concentrationof the polymerization mixture until the solid content is between about0.01 to 10% or between about 18 to 60%; and d. adding at least onecross-linking agent to the polymerization mixture to form saidnano-strings having a poly(alkenylbenzene) core and a poly(conjugateddiene) surface.
 2. The process of claim 1 wherein step a comprisesperformed in the presence of a functionalized lithium initiator.
 3. Theprocess of claim 1 further including a hydrogenation step convertingsaid poly(conjugated diene) surface to a poly(alkylene) surface.
 4. Theprocess of claim 1 further including polymerization of alkenylbenzene toform a mono-block polymer.
 5. The process of claim 4 wherein the ratioof said mono-block polymer to said diblock copolymers is controlled byselective addition of initiator and optionally a further monomeraddition.
 6. The process of claim 1 wherein said diblock polymerincludes a poly(alkenylbenzene) block and a copolymer block.
 7. Theprocess of claim 1, wherein the alkenylbenzene comprises a member of thegroup consisting of: styrene, α-methyl-styrene, 1-vinyl naphthalene,2-vinyl naphthalene, vinyl toluene, methoxystyrene, t-butoxystyrene, thealkyl, cycloalkyl, aryl, alkaryl, and aralkyl derivatives thereof inwhich the total number of carbon atoms in the alkenylbenzene comprisesabout 18 or fewer, and mixtures thereof.
 8. The process of claim 1,wherein the conjugated diene comprises 1,3-butadiene, isoprene, or 1,3pentadiene.
 9. The process of claim 1, wherein a functionality of thecross-linking agent comprises at least bifunctional.
 10. The process ofclaim 9, wherein the cross-linking agent comprises divinylbenzene. 11.The process of claim 1, further wherein the polymerizing alkenylbenzeneand conjugated diene occurs in the presence of a randomizing modifier.12. The process of claim 11, wherein the randomizing modifier comprisesone from the group: hexamethylphosphoric acid triamide, N,N,N′,N′-tetramethylethylene diamene, ethylene glycol dimethyl ether,diethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, tetrahydrofuran,1,4-diazabicyclo[2.2.2]octane, diethyl ether, triethylamine,tri-n-butylamine, tri-n-butylphosphine, p-dioxane, 1,2 dimethoxy ethane,dimethyl ether, methyl ethyl ether, ethyl propyl ether, di-n-propylether, di-n-octyl ether, anisole, dibenzyl ether, diphenyl ether,dimethylethylamine, bix-oxalanyl propane, tri-n-propyl amine, trimethylamine, triethyl amine, N,N-dimethyl aniline, N-ethylpiperidine,N-methyl-N-ethyl aniline, N-methylmorpholine, tetramethylenediamine,oligomeric oxolanyl propanes (OOPs), 2,2-bis-(4-methyl dioxane),bistetrahydrofuryl propane, and mixtures thereof.
 13. The process ofclaim 11, wherein a ratio of the randomizing modifier to the monomerscomprises less than about 400 millimoles of randomizing modifier perhundred grams of monomer.
 14. The process of claim 3, wherein thehydrogenation step comprises hydrogenation in the presence of ahydrogenation catalyst.
 15. The process of claim 14, wherein thehydrogenation catalyst comprises at least one of the group consisting ofPt, Pd, Rh, Ru, Ni, nickel octolate, nickel ethylhexanoate, and mixturesthereof.
 16. The process of claim 3, wherein the hydrogenation stepcomprises at least 20% conversion.
 17. The process of claim 1, whereinstep a comprises performed in the presence of an initiator comprisingone of the group consisting of: ethyllithium, propyllithium,n-butyllithium, sec-butyllithium, tert-butyllithium, aryllithiums, suchas phenyllithium, tolyllithium, alkenyllithiums such as vinyllithium,propenyllithium, alkylene lithium such as tetramethylene lithium,pentamethylene lithium, p-tolyllithium, 4-phenylbutyl lithium,4-butylcyclohexyl lithium, 4-cyclohexylbutyl lithium, lithium dialkylamines, lithium dialkyl phosphines, lithium alkyl aryl phosphine, andlithium diaryl phosphines.
 18. The process of claim 2, wherein thefunctionalized lithium initiator comprises an amine-functionalizedlithium initiator, comprising the formula:(A)Li(SOL)_(y) where y comprises from about 1 to about 3, SOL comprisesone of the group consisting of hydrocarbons, ethers, amines, andmixtures thereof, and A comprises one of the group consisting of alkyl,dialkyl, and cycloalkyl amine radicals comprising the formula:

and cyclic amines comprising the formula:

where R¹ comprises one of the group consisting of alkyls, cycloalkyls,and aralkyls comprising from about 1 to about 12 carbon atoms, and R²comprises one of the group consisting of alkylene, substituted alkylene,oxy-alkylamino-alkylene and N-alkylamino-alkylene comprising from about3 to about 16 methylene groups.
 19. The process of claim 18, wherein thefunctionalized lithium initiator comprises hexamethylene iminepropyllithium.
 20. The process of claim 2, wherein the functionalizedlithium initiator comprises a tin functionalized lithium initiator.